U.S. patent application number 15/562387 was filed with the patent office on 2018-10-04 for method of manufacturing grain-oriented electrical steel sheet.
This patent application is currently assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION. The applicant listed for this patent is NIPPON STEEL & SUMITOMO METAL CORPORATION. Invention is credited to Shin FURUTAKU, Naoto MASUMITSU, Nobusato MORISHIGE, Hirotoshi TADA, Masaru TAKAHASHI, Junichi TAKAOBUSHI.
Application Number | 20180282830 15/562387 |
Document ID | / |
Family ID | 57004484 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180282830 |
Kind Code |
A1 |
TADA; Hirotoshi ; et
al. |
October 4, 2018 |
METHOD OF MANUFACTURING GRAIN-ORIENTED ELECTRICAL STEEL SHEET
Abstract
Provided is a method of manufacturing a grain-oriented
electrical steel sheet including: a heating process of heating a
slab having a predetermined chemical composition at T1.degree. C.
of 1150.degree. C. to 1300.degree. C., retaining the slab for 5
minutes to 30 hours, lowering the temperature of the slab to
T2.degree. C. of T1-50.degree. C. or lower, heating the slab at
T3.degree. C. of 1280.degree. C. to 1450.degree. C., and retaining
the slab for 5 minutes to 60 minutes; a hot-rolling process of
hot-rolling the slab that is heated to obtain a hot-rolled steel
sheet; a cold-rolling process; an intermediate annealing process of
performing intermediate annealing with respect to the hot-rolled
steel sheet at least one time before the cold-rolling process or
before a final pass of the cold-rolling process after interrupting
the cold-rolling; an annealing separating agent applying process;
and a secondary film applying process. In the cold-rolling process,
a retention treatment is performed during a plurality of passes. In
the retention treatment, retention at a temperature T.degree. C.
satisfying 170+[Bi].times.5000.ltoreq.T.ltoreq.300 is performed one
time to four times. A heating rate in the decarburization annealing
process is 50.degree. C./second or faster.
Inventors: |
TADA; Hirotoshi;
(Himeji-shi, JP) ; MORISHIGE; Nobusato; (Kobe-shi,
JP) ; MASUMITSU; Naoto; (Narashino-shi, JP) ;
TAKAOBUSHI; Junichi; (Himeji-shi, JP) ; FURUTAKU;
Shin; (Himeji-shi, JP) ; TAKAHASHI; Masaru;
(Nishinomiya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL & SUMITOMO METAL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NIPPON STEEL & SUMITOMO METAL
CORPORATION
Tokyo
JP
|
Family ID: |
57004484 |
Appl. No.: |
15/562387 |
Filed: |
April 1, 2016 |
PCT Filed: |
April 1, 2016 |
PCT NO: |
PCT/JP2016/060921 |
371 Date: |
September 27, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 6/008 20130101;
C22C 38/60 20130101; C21D 8/1233 20130101; C22C 38/16 20130101;
C21D 8/1222 20130101; C21D 8/1272 20130101; C21D 8/1283 20130101;
H01F 1/16 20130101; C22C 38/00 20130101; H01F 1/18 20130101; C21D
8/1261 20130101; C22C 38/02 20130101; C21D 2201/05 20130101; C22C
38/008 20130101; C21D 9/46 20130101; C22C 38/12 20130101; C21D 8/12
20130101; C21D 8/1255 20130101 |
International
Class: |
C21D 6/00 20060101
C21D006/00; C21D 8/12 20060101 C21D008/12; C21D 9/46 20060101
C21D009/46; C22C 38/16 20060101 C22C038/16; C22C 38/02 20060101
C22C038/02; C22C 38/60 20060101 C22C038/60; C22C 38/00 20060101
C22C038/00; C22C 38/12 20060101 C22C038/12; H01F 1/18 20060101
H01F001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2015 |
JP |
2015-075839 |
Claims
1. A method of manufacturing a grain-oriented electrical steel
sheet, comprising: a heating process of heating a slab, which
contains, in terms of mass %, C: 0.030% to 0.150%, Si: 2.50% to
4.00%, Mn: 0.02% to 0.30%, one or two of S and Se: 0.005% to 0.040%
in a total amount, an acid-soluble Al: 0.015% to 0.040%, N: 0.0030%
to 0.0150%, Bi: 0.0003% to 0.0100%, Sn: 0% to 0.50%, Cu: 0% to
0.20%, one or two of Sb and Mo: 0% to 0.30% in a total amount, and
the remainder including Fe and impurities, to T1.degree. C. of
1150.degree. C. to 1300.degree. C., retaining the slab for 5
minutes to 30 hours, lowering the temperature of the slab to
T2.degree. C. of T1-50.degree. C. or lower, heating the slab at
T3.degree. C. of 1280.degree. C. to 1450.degree. C., and retaining
the slab for 5 minutes to 60 minutes; a hot-rolling process of
hot-rolling the slab that is heated to obtain a hot-rolled steel
sheet, a cold-rolling process of performing a cold-rolling
including a plurality of passes with respect to the hot-rolled
steel sheet to obtain a cold-rolled steel sheet having a sheet
thickness of 0.30 mm or less; an intermediate annealing process of
performing an intermediate annealing with respect to the hot-rolled
steel sheet at least one time before the cold-rolling process or
before a final pass of the cold-rolling process after interrupting
the cold-rolling; a decarburization annealing process of
decarburization annealing with respect to the cold-rolled steel
sheet; an annealing separating agent applying process of applying
an annealing separating agent to the cold-rolled steel sheet after
the decarburization annealing; a final annealing process of
performing a final annealing with respect to the cold-rolled steel
sheet after the annealing separating agent applying process; and a
secondary film applying process of applying an insulating film onto
the cold-rolled steel sheet after the final annealing, wherein in
the intermediate annealing process, the intermediate annealing, in
which a retention is performed at a temperature of 1000.degree. C.
to 1200.degree. C. for 5 seconds to 180 seconds, is performed, in
the cold-rolling process, a retention treatment, in which the
hot-rolled steel sheet is retained one or more times at a
temperature of 130.degree. C. to 300.degree. C. for 3 minutes to
120 minutes, is performed during the plurality of passes, in the
retention treatment, a retention at a temperature TOC satisfying
the following Expression (1) is performed one time to four times,
and a heating rate in the decarburization annealing process is
50.degree. C./second or faster,
170+[Bi].times.5000.ltoreq.T.ltoreq.300 (1) (here, [Bi] in
Expression (1) represents the amount of Bi in terms of mass % in
the slab).
2. The method of manufacturing a grain-oriented electrical steel
sheet according to claim 1, wherein the slab contains, in terms of
mass %, Sn: 0.05% to 0.50%.
3. The method of manufacturing a grain-oriented electrical steel
sheet according to claim 1 or 2, wherein the slab contains, in
terms of mass %, Cu: 0.01% to 0.20%.
4. The method of manufacturing a grain-oriented electrical steel
sheet according to claim 1 or 2, wherein the slab contains, in
terms of mass %, one or two of Sb and Mo in a total amount of
0.0030% to 0.30%.
5. The method of manufacturing a grain-oriented electrical steel
sheet according to claim 1 or 2, wherein in the final annealing
process, an X value, which is calculated with the following
Expression (2), is set to 0.0003 Nm.sup.3/(hm.sup.2) or greater,
X=Atmosphere gas flow rate/total steel sheet surface area (2),
6. The method of manufacturing a grain-oriented electrical steel
sheet according to claim 3, wherein the slab contains, in terms of
mass %, one or two of Sb and Mo in a total amount of 0.0030% to
0.30%.
7. The method of manufacturing a grain-oriented electrical steel
sheet according to claim 3, wherein in the final annealing process,
an X value, which is calculated with the following Expression (2),
is set to 0.0003 Nm.sup.3/(hm.sup.2) or greater, X=Atmosphere gas
flow rate/total steel sheet surface area (2).
8. The method of manufacturing a grain-oriented electrical steel
sheet according to claim 4, wherein in the final annealing process,
an X value, which is calculated with the following Expression (2),
is set to 0.0003 Nm.sup.3/(hm.sup.2) or greater, X=Atmosphere gas
flow rate/total steel sheet surface area (2).
9. The method of manufacturing a grain-oriented electrical steel
sheet according to claim 6, wherein in the final annealing process,
an X value, which is calculated with the following Expression (2),
is set to 0.0003 Nm.sup.3/(hm.sup.2) or greater, X=Atmosphere gas
flow rate/total steel sheet surface area (2).
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a method of manufacturing a
grain-oriented electrical steel sheet.
[0002] Priority is claimed on Japanese Patent Application No.
2015-075839, filed on Apr. 2, 2015, the content of which is
incorporated herein by reference.
RELATED ART
[0003] The grain-oriented electrical steel sheet is mainly used as
an iron core material of a stationary induction apparatus such as a
transformer. According to this, the grain-oriented electrical steel
sheet is demanded to have characteristics such as a characteristic
in which an energy loss (that is, an iron loss) when being excited
with an alternating current is low, a characteristic in which
permeability is high and excitation is easy, and a characteristic
in which magnetostriction that becomes a cause of noise is small.
In the related art, various developments have been made to
manufacture the grain-oriented electrical steel sheet that
satisfies the above-described characteristics. As a result, for
example, as described in Patent Document 1, particularly, an
improvement of a {110}<001> orientation integration degree in
a steel sheet has a great effect.
[0004] To improve the {110}<001> orientation integration
degree in the steel sheet, it is important to suppress normal grain
growth in primary recrystallization and to subject only
{110}<001> orientation particles to abnormal grain growth in
the subsequent secondary recrystallization. For this, it is
effective to accurately control an in-steel fine precipitate or a
grain boundary precipitation element called an inhibitor.
[0005] As a method of realizing the above control, there is known a
technology in which the inhibitor is solutionized through slab
heating, and the inhibitor is uniformly and finely precipitated in
a hot-rolling process, a hot-rolled sheet annealing process, and an
intermediate annealing process as subsequent processes. As the
inhibitor, for example. Patent Document 1 discloses a method of
controlling MnS and AlN, Patent Document 2 discloses a method of
controlling MnS and MnSe, and Patent Document 3 discloses a method
of controlling CuxS, CuxSe, or Cux (Sc, S) and (Al, Si)N.
[0006] However, in technologies described in Patent Document 1 to
Patent Document 3, there is a problem that it is difficult to
stably obtain excellent magnetic characteristics.
[0007] Patent Document 4 discloses a measure for adding Bi in a
slab in a manufacturing method for stably obtaining an
ultra-high-magnetic-flux-density grain-oriented electrical steel
sheet. However, when steel contains Bi, there is a problem that
deterioration in adhesiveness of a primary film occurs or a primary
film is less likely to be formed, by Bi contained in the steel.
Therefore, in the technology described in Patent Document 4, even
though satisfactory magnetic characteristics are obtained,
formation of the primary film may not be sufficient in some
cases.
[0008] In addition, Patent Document 5 to be described below
discloses a technology of improving magnetic characteristics by
performing an aging treatment in a process of cold-rolling a steel
sheet, which is obtained after annealing of a hot-rolled steel
sheet that contains Bi, to a target sheet thickness. However, in
Patent Document 5, examination is not made on the film
adhesiveness, and it is not clear that the aging treatment has any
effect on the primary film.
[0009] Patent Document 6 discloses a technology of forming a
satisfactory primary film. In the technology, a cold-rolled sheet
that contains Bi is heated to 700.degree. C. or higher at a rate of
100.degree. C./second or faster or is heated to 700.degree. C. or
higher within 10 seconds. Then, preliminary annealing, in which
retention is performed at a temperature of 700.degree. C. or higher
for 1 second to 20 seconds, is performed, and decarburization
annealing is performed. Then, the amount of TiO.sub.2, which is
added in an annealing separating agent that is subsequently
applied, is increased. However, in the technology disclosed in
Patent Document 6, there are lots of problems such as a problem of
significantly increasing an addition amount of TiO.sub.2 or an
application amount of the annealing separating agent in order that
a film is not peeled off even when a product is bent along a round
bar of 20 mm.PHI..
PRIOR ART DOCUMENT
Patent Document
[0010] [Patent Document 1] Japanese Examined Patent Application.
Second Publication No. S40-15644
[0011] [Patent Document 2] Japanese Examined Patent Application,
Second Publication No. S51-13469
[0012] [Patent Document 3] Japanese Unexamined Patent Application,
First Publication No. H10-102149
[0013] [Patent Document 4] Japanese Unexamined Patent Application.
First Publication No. H6-88171
[0014] [Patent Document 5] Japanese Unexamined Patent Application,
First Publication No. H8-253816
[0015] [Patent Document 6] Japanese Unexamined Patent Application,
First Publication No. 2003-096520
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0016] The present invention has been made in consideration of the
above-described problems, and an object thereof is to provide a
method of manufacturing a grain-oriented electrical steel sheet
which is capable of obtaining the grain-oriented electrical steel
sheet having excellent magnetic characteristics at a low cost while
improving adhesiveness of a primary film.
Means for Solving the Problem
[0017] The present inventors have made a thorough investigation on
slab heating conditions, steel sheet retention conditions in a
cold-rolling process, an effect due to a heating rate in
decarburization annealing, and the like to solve the
above-described problems. As a result, it is found that
adhesiveness of the primary film is improved by lowering a slab
temperature during slab heating, and the slab is reheated and
rolled, by retaining a steel sheet in a predetermined temperature
range in the cold-rolling process, and by controlling the heating
rate appropriately in the decarburization annealing process.
[0018] The present invention to be described below in detail is
accomplished on the basis of the above-described finding, and the
gist of the present invention is as follows.
[0019] (1) According to an aspect of the present invention, there
is provided a method of manufacturing a grain-oriented electrical
steel sheet. The method including: a heating process of heating a
slab, which contains, in terms of mass %. C: 0.030% to 0.150%, Si:
2.50% to 4.00%, Mn: 0.02% to 0.30%, one or two of S and Se: 0.005%
to 0.040% in a total amount, an acid-soluble Al: 0.015% to 0.040%,
N: 0.0030% to 0.015%, Bi: 0.0003% to 0.0100%, Sn: 0% to 0.50%. Cu:
0% to 0.20%, one or two of Sb and Mo: 0% to 0.30% in a total
amount, and the remainder including Fe and impurities, to
T1.degree. C. of 1150.degree. C. to 1300.degree. C., retaining the
slab for 5 minutes to 30 hours, lowering the temperature of the
slab to T2.degree. C. of T1-50.degree. C. or lower, heating the
slab at T3.degree. C. of 1280.degree. C. to 1450.degree. C., and
retaining the slab for 5 minutes to 60 minutes; a hot-rolling
process of hot-rolling the slab that is heated to obtain a
hot-rolled steel sheet; a cold-rolling process of performing a
plurality of passes of cold-rolling with respect to the hot-rolled
steel sheet to obtain a cold-rolled steel sheet having a sheet
thickness of 0.30 mm or less; an intermediate annealing process of
performing intermediate annealing with respect to the hot-rolled
steel sheet at least one time before the cold-rolling process or
before a final pass of the cold-rolling process by stopping the
cold-rolling; a decarburization annealing process of subjecting the
cold-rolled steel sheet to decarburization annealing, an annealing
separating agent applying process of applying an annealing
separating agent to the cold-rolled steel sheet obtained after the
decarburization annealing; a final annealing process of performing
final annealing with respect to the cold-rolled steel sheet
obtained after the annealing separating agent applying process; and
a secondary film applying process of applying an insulating film
onto the cold-rolled steel sheet obtained after the final
annealing. In the intermediate annealing process, the intermediate
annealing, in which retention is performed at a temperature of
1000.degree. C. to 1200.degree. C. for 5 seconds to 180 seconds, is
performed during the plurality of passes. In the cold-rolling
process, a retention treatment, in which the hot-rolled steel sheet
is retained one or more times at a temperature of 130.degree. C. to
300.degree. C. for 3 minutes to 120 minutes, is performed. In the
retention treatment, retention at a temperature T.degree. C.
satisfying Expression (a) is performed one time to four times. A
heating rate in the decarburization annealing process is 50.degree.
C./second or faster.
170+[Bi].times.5000.ltoreq.T.ltoreq.300 (a)
(here, [Bi] in Expression (1) represents the amount of Bi in terms
of mass % in the slab)
[0020] (2) In the method of manufacturing a grain-oriented
electrical steel sheet according to (1), the slab may contain, in
terms of mass %, Sn: 0.05% to 0.50%.
[0021] (3) In the method of manufacturing a grain-oriented
electrical steel sheet according to (1) or (2), the slab may
contain, in terms of mass %, Cu: 0.01% to 0.20%.
[0022] (4) In the method of manufacturing a grain-oriented
electrical steel sheet according to any one of (1) to (3), the slab
may contain, in terms of mass %, one or two of Sb and Mo in a total
amount of 0.0030% to 0.30%.
[0023] (5) In the method of manufacturing a grain-oriented
electrical steel sheet according to any one of (1) to (4), in the
final annealing process, an X value, which is calculated with
Expression (b), may be set to 0.0003 Nm.sup.3/(hm.sup.2) or
greater.
X=Atmosphere gas flow rate/total steel sheet surface area (b)
Effects of the Invention
[0024] According to the aspect of the present invention, it is
possible to obtain a grain-oriented electrical steel sheet having
excellent magnetic characteristics while improving adhesiveness of
a primary film at a low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a graph illustrating a relationship between the
highest temperature in an aging treatment and an amount of Bi in
Examples.
[0026] FIG. 2 is a graph illustrating a relationship between the
number of times of aging treatments satisfying Expression (1) and
the number of times of aging treatments at 130.degree. C. to
300.degree. C. in Examples.
[0027] FIG. 3 is a graph illustrating preferable ranges of a
heating rate in decarburization annealing and a hot-rolled sheet
annealing temperature in Examples.
EMBODIMENTS OF THE INVENTION
[0028] Hereinafter, a method of manufacturing a grain-oriented
electrical steel sheet according to an embodiment of the present
invention (may be referred to as a method of manufacturing a
grain-oriented electrical steel sheet according to this embodiment)
will be described in detail.
[0029] (With Respect to Chemical Composition of Steel)
[0030] First, description will be given of a chemical composition
(chemical component) of steel that is used in the method of
manufacturing the grain-oriented electrical steel sheet according
to this embodiment.
[0031] In the method of manufacturing the grain-oriented electrical
steel sheet according to this embodiment, a slab, which contains,
in terms of mass %, C: 0.030% to 0.150%, Si: 2.50% to 4.00%, Mn:
0.02% to 0.30%, one or two of S and Se: 0.005% to 0.040% in a total
amount, an acid-soluble Al: 0.015% to 0.04%, N: 0.0030% to 0.0150%,
Bi: 0.0003% to 0.0100%, and the remainder including Fe and
impurities, is used.
[0032] Basically, the slab, which is used in the method of
manufacturing the grain-oriented electrical steel sheet according
to this embodiment, contains the above-described elements, and the
remainder including Fe and impurities. However, the slab may
further contain 0.05 to 0.50 mass % of Sn instead of a part of Fe.
In addition, the slab may further contain 0.01 to 0.20 mass % of Cu
instead of a part of Fe. In addition, the slab may further contain
one or two of Sb and Mo in a total amount of 0.0030 to 0.30 mass %
instead of a part of Fe. However, Sn. Cu, Sb, and Mo may not be
contained. Accordingly, the lower limit of these elements is
0%.
[0033] (C: 0.030% to 0.150%)
[0034] When the amount of C (carbon) is less than 0.030%, a crystal
grain abnormally grows when heating the slab prior to hot-rolling.
As a result, secondary recrystallization failure called a linear
fine grain occurs in a product. On the other hand, when the amount
of C is greater than 0.150%, in decarburization annealing that is
performed after cold-rolling process, a long decarburization time
is necessary, and is not economical. In addition, decarburization
is likely to be incomplete. When the decarburization is incomplete,
magnetic failure called magnetic aging occurs in a product.
Therefore, the incomplete decarburization is not preferable.
Accordingly, the amount of C is set to 0.030%0 to 0.150%, and
preferably 0.050% to 0.100%.
[0035] (Si: 2.50% to 4.00%)
[0036] Si (silicon) is an element that is very effective to reduce
an eddy current loss that partially constitutes an iron loss by
increasing electrical resistance of steel. However, in a case where
the amount of Si is less than 2.50%, it is difficult to suppress
the eddy current loss of a product. On the other hand, when the
amount of Si is greater than 4.00%, workability of steel
significantly deteriorates, and cold-rolling at room temperature
becomes difficult. Accordingly, the amount of Si is set to 2.50% to
4.00%, and preferably 2.90% to 3.60%.
[0037] (Mn: 0.02% to 0.30%)
[0038] Mn (manganese) is an important element that forms MnS and/or
MnSe which are compounds called an inhibitor that influences
secondary recrystallization. In a case where the amount of Mn is
less than 0.02%, an absolute amount of MnS and/or MnSe necessary
for causing secondary recrystallization to occur becomes deficient.
Accordingly, this range is not preferable. On the other hand, in a
case where amount of Mn is greater than 0.30%, since solid-solution
of Mn becomes difficult when heating the slab, the amount of MnS
and/or MnSe which precipitate decreases, and a precipitation size
is likely to be coarse. Therefore, an optimal size distribution as
an inhibitor is damaged. Accordingly, the amount of Mn is set to
0.02% to 0.30%, and preferably 0.05% to 0.25%.
[0039] (S and/or Se: 0.005% to 0.040% in Total Amount)
[0040] S (sulfur) is an important element that reacts with Mn to
form MnS that is an inhibitor, and Se (selenium) is an important
element that reacts with Mn to form MnSe that is an inhibitor. MnS
and MnSe have the same effect as an inhibitor. Accordingly, as long
as the total amount of S and Se is in a range of 0.005% to 0.04%,
any one of S and Se may be contained, and both of S and Se may be
contained. On the other hand, in a case where the total amount of S
and/or Se (the total amount of one or two of S and Se) is less than
0.005%, or in a case where the total amount of S and Se is greater
than 0.040%, it is difficult to obtain a sufficient inhibitor
effect. Accordingly, it is necessary to set the total amount of S
and/or Se to 0.005% to 0.040%. The total amount of S and/or Se is
preferably 0.010 to 0.035%.
[0041] (Acid-Soluble Al: 0.015% to 0.040%)
[0042] Acid-soluble aluminum (sol. Al) is a constituent element of
AlN that is an inhibitor important to obtain a
high-magnetic-flux-density grain-oriented electrical steel sheet.
When the amount of acid-soluble Al is less than 0.015%, the amount
of an inhibitor becomes deficient, and inhibitor strength becomes
deficient. On the other hand, in a case where the amount of
acid-soluble Al is greater than 0.040%, AlN that precipitates as an
inhibitor becomes coarse. As a result, inhibitor strength
decreases. Accordingly, the amount of acid-soluble Al is set to
0.015% to 0.040%, and preferably 0.018% to 0.035%.
[0043] (N: 0.0030% to 0.0150%)
[0044] N (nitrogen) is an important element that reacts with
acid-soluble Al to form AlN. In a case where the amount of N is
less than 0.0030%, or in a case where the amount of N is greater
than 0.0150%, it is difficult to obtain a sufficient inhibitor
effect. Accordingly, the amount of N is limited to 0.0030% to
0.0150%, and preferably 0.0050% to 0.0120%.
[0045] (Bi: 0.0003% to 0.0100%)
[0046] Bi (bismuth) is an essential element that is contained in
the slab in order to obtain an excellent magnetic flux density in
manufacturing of the grain-oriented electrical steel sheet
according to this embodiment. When the amount of Bi is less than
0.0003%, it is difficult to sufficiently obtain a magnetic flux
density improving effect. On the other hand, when the amount of Bi
is greater than 0.0100%, the magnetic flux density improving effect
is saturated, and there is a high possibility that adhesion failure
of a primary film may occur. Accordingly, the amount of Bi is set
to 0.0003% to 0.0100%, preferably 0.0005% to 0.0090%, and more
preferably 0.0007% to 0.0080%.
[0047] (Sn: 0% to 0.50%)
[0048] Sn (tin) is not necessary to be contained, but Sn is an
element that is effective to stably attain secondary
recrystallization of a thin product. In addition. Sn is an element
having effect of making a secondary recrystallized grain be small.
To obtain these effects, it is necessary to contain 0.05% or
greater of Sn. Accordingly, in a case where Sn is contained, it is
preferable that the amount of Sn is set to 0.05% or greater. In
addition, even when the amount of Sn is greater than 0.50%, the
effect is saturated. According to this, even in a case where Sn is
contained, it is preferable that the amount of Sn is set to 0.50%
or less from the viewpoint of the cost. The amount of Sn is more
preferably 0.08% to 0.30%.
[0049] (Cu: 0.degree. % to 0.20%)
[0050] Cu (copper) is not necessary to be contained, but Cu is an
element that is effective to improve a primary film of steel that
contains Sn. In a case where the amount of Cu is less than 0.01%,
an effect of improving the primary film is small. Accordingly, it
is preferable that the amount of Cu is set to 0.01% or greater to
obtain the effect. On the other hand, when the amount of Cu is
greater than 0.20%, a magnetic flux density decreases. Therefore,
this range is not preferable. Accordingly, even when Cu is
contained, it is preferable that the amount of Cu is set to 0.01%
to 0.20%, and more preferably 0.03% to 0.18%.
[0051] [Sb and/or Mo: 0% to 0.30% in Total Amount]
[0052] Sb (antimony) and Mo (molybdenum) are not necessary to be
contained, but Sb and Mo are effective for stably obtaining
secondary recrystallization of a thin product. To obtain this
effect in a more reliable manner, it is preferable that the total
amount of Sb and/or Mo (the total amount of one or two of Sb and
Mo) is set to 0.0030% or greater. Any one of Sb and Mo may be
contained, or both of Sb and Mo may be contained. On the other
hand, when the total amount of Sb and/or Mo is greater than 0.30%,
the above-described effect is saturated. Accordingly, even when
being contained, it is preferable that the total amount of Sb
and/or Mo is set to 0.30% or less, and more preferably 0.0050% to
0.25%.
[0053] (With Respect to Manufacturing Process of Grain-Oriented
Electrical Steel Sheet)
[0054] Next, manufacturing processes included in the method of
manufacturing the grain-oriented electrical steel sheet according
to this embodiment will be described in detail. According to the
manufacturing method including manufacturing processes to be
described below, it is possible to provide a grain-oriented
electrical steel sheet that is used in an iron core material of a
transformer and the like and has sufficient magnetic
characteristics at a low cost.
[0055] <Heating Process>
[0056] The slab, of which components are adjusted in the
above-described ranges, is heated prior to hot-rolling. The slab is
obtained by casting molten steel of which components are adjusted
in the above-described ranges. A casting method is not particularly
limited, and a casting method of molten steel for manufacturing of
a typical grain-oriented electrical steel sheet may be applied.
[0057] In a method of manufacturing the grain-oriented electrical
steel sheet according to this embodiment, when heating the slab
having the above described components, the slab is heated to
T1.degree. C. of 1150.degree. C. to 1300.degree. C., and is
retained (soaked) at T1.degree. C. for 5 minutes to 30 hours. Then,
the temperature of the slab is lowered to T2.degree. C. that is
equal to or lower than T1-50.degree. C. (that is, T1-T2.gtoreq.50).
Then, the slab is heated again to T3.degree. C. of 1280.degree. C.
to 1450.degree. C., and is retained at T3.degree. C. for 5 minutes
to 60 minutes. In a case where T1 is lower than 1150.degree. C., T3
is lower than 1280.degree. C. or the retention time at T1.degree.
C. and/or T3.degree. C. is shorter than 5 minutes, it is difficult
to obtain desired magnetic characteristics. Particularly, the
magnetic characteristics are greatly affected by the retention
temperature after the reheating. Accordingly, T3 is preferably
1300.degree. C. or higher. On the other hand, when the heating
temperature is too high, a special facility is necessary.
Therefore, the manufacturing costs increase. According to this, T3
is preferably 1400.degree. C. or lower.
[0058] In addition, when the retention time at T1.degree. C. or
T3.degree. C. is long, productivity deteriorates, and thus, the
manufacturing cost increases. According to this, the retention time
at T1.degree. C. is set to 30 hours or shorter, and preferably 25
hours or shorter. In addition, the retention time at T3.degree. C.
is 60 minutes or shorter, and preferably 50 minutes or shorter.
[0059] In addition, in a case where T1-T2 is less than 50.degree.
C. (T1-T2<50), film adhesiveness deteriorates. This mechanism is
not clear, but it is considered that the deterioration is caused by
a variation in a surface quality of a steel sheet due to a
variation in a behavior of scale formation and descaling during
slab heating and hot-rolling. On the other hand, when T1-T2 is too
great, special facility is necessary for heating from T2.degree. C.
to T3.degree. C. Accordingly, it is preferable that T1-T2 is set to
200.degree. C. or lower. That is, it is preferable to satisfy a
relationship of 50.ltoreq.T1-T2.ltoreq.200.
[0060] In this embodiment, the temperature of the slab is a surface
temperature. In addition, temperature lowering from T1.degree. C.
to T2.degree. C. may be performed by any method such as water
cooling and air cooling, but the air cooling (radiation cooling) is
preferable.
[0061] <Hot-Rolling Process>
[0062] The slab, which is heated in the heating process, is
hot-rolled to obtain a hot-rolled steel sheet. Conditions of the
hot-rolling are not particularly limited and conditions which are
applied to a typical grain-oriented electrical steel sheet may be
employed.
[0063] <Cold-Rolling Process>
[0064] In a cold-rolling process, cold-rolling including a
plurality of passes is performed to obtain a cold-rolled steel
sheet having a sheet thickness of 0.30 mm or less. In a case where
the sheet thickness after the cold-rolling process is greater than
0.30 mm, an iron loss deteriorates. Accordingly, the sheet
thickness after the cold-rolling process is set to 0.30 mm or less,
and preferably 0.27 mm or less. Furthermore, the lower limit of the
sheet thickness after the cold-rolling process is not particularly
limited, but it is preferable that the thickness is set to, for
example, 0.10 mm or greater, and more preferably 0.15 mm or
greater.
[0065] In addition, in the cold-rolling process, a retention
treatment (aging treatment), in which the steel sheet is retained
at a temperature of 130.degree. C. to 300.degree. C. for 3 minutes
to 120 minutes, is performed one or more times during the passes.
However, in a plurality of the retention treatments, it is
necessary to perform a retention treatment (aging treatment) at a
temperature TOC satisfying the following Expression (1) for 3
minutes to 120 minutes one time to four times during the
retention.
170+[Bi].times.5000.ltoreq.T.ltoreq.300 (1)
[0066] Here, [Bi] in Expression (1) represents the amount of Bi in
the slab (unit: mass %).
[0067] In a case where the aging treatment is not performed, the
aging treatment temperature is lower than 130.degree. C., or the
retention time is shorter than 3 minutes, it is difficult to attain
desired magnetic characteristics. On the other hand, in a case
where the aging treatment temperature is higher than 300.degree. C.
a special facility is necessary, and the manufacturing cost
increases. Therefore, this range is not preferable. In addition,
when the retention time is longer than 120 minutes, productivity
deteriorates, and the manufacturing cost increases. Therefore, this
range is not preferable.
[0068] In addition, even in a case where the aging treatment is
performed one or more times under the above conditions, when the
aging treatment satisfying Expression (1) is not performed or the
aging treatment satisfying Expression (1) is performed more than
four times, film adhesiveness deteriorates. Preferable aging
treatment conditions are as in the following Expression (1).
[0069] It is preferable that the retention treatment (aging
treatment) of the cold-rolling process is performed under the
following conditions instead of the above-described conditions.
That is, it is preferable that an aging treatment to retain at a
temperature of 140.degree. C. to 300.degree. C. for 5 minutes to
120 minutes is performed two or more times, and an aging treatment
to retain at a temperature T.degree. C. satisfying the following
Expression (1') for 5 minutes to 120 minutes is performed one time
to four times. When satisfying the conditions, the film
adhesiveness is improved in more stable manner.
175+[Bi].times.5000.ltoreq.T.ltoreq.300 (1')
[0070] <Intermediate Annealing Process>
[0071] Before the cold-rolling process (between the hot-rolling
process and the cold-rolling process) or during a plurality of
passes of the cold-rolling process (before the final pass of the
cold-rolling process after interrupting the cold-rolling process at
once), intermediate annealing is performed with respect to the
hot-rolled steel sheet at least one time (preferably one time or
two times). That is, cold-rolling is performed after annealing
(so-called hot-rolled sheet annealing) is performed with respect to
the hot-rolled steel sheet before the cold-rolling, the plurality
of passes of cold-rolling including intermediate annealing are
performed without performing the hot-rolled sheet annealing, or the
plurality of passes of cold-rolling including intermediate
annealing are performed after the hot-rolled sheet annealing.
[0072] In the intermediate annealing process, annealing in which
retention is performed at a temperature of 1000.degree. C. to
1200.degree. C. for 5 seconds to 180 seconds is performed. In a
case where the annealing temperature is lower than 1000.degree. C.,
it is difficult to obtain desired magnetic characteristics and film
adhesiveness. On the other hand, in a case where the temperature is
higher than 1200.degree. C., special facility is necessary, and the
manufacturing cost increases. Accordingly the annealing temperature
is set to 1000.degree. C. to 1200.degree. C., and preferably
1030.degree. C. to 1170.degree. C.
[0073] In addition, in a case where the annealing time is shorter
than 5 seconds, it is difficult to obtain desired magnetic
characteristics and film adhesiveness. On the other hand, in a case
where the annealing time is longer than 180 seconds, special
facility is necessary and the manufacturing cost increases.
Accordingly, in this embodiment, the annealing time is set to 5
seconds to 180 seconds, and preferably 10 seconds to 120
seconds.
[0074] <Decarburization Annealing Process>
[0075] Decarburization annealing is performed with respect to the
cold-rolled steel sheet after the cold-rolling process. Here, a
heating rate during heating in the decarburization annealing is set
to 50.degree. C./second or faster. With regard to the heating
temperature, the heating time, and the like in the decarburization
annealing, conditions which are applied to a typical grain-oriented
electrical steel sheet may be employed.
[0076] In a case where the heating rate in the decarburization
annealing is slower than 50.degree. C./second, it is difficult to
obtain desired magnetic characteristics and film adhesiveness.
Accordingly, the heating rate is set to 50.degree. C./second or
faster, and preferably 80.degree. C./second or faster. The upper
limit of the heating rate is not particularly limited, but special
facility is necessary to excessively raise the heating rate.
Therefore, the heating rate is set to 2000.degree. C./second or
slower.
[0077] <Annealing Separating Agent Applying Process>
[0078] <Final Annealing Process>
[0079] An annealing separating agent is applied onto the
cold-rolled steel sheet after the decarburization annealing, and
final annealing is performed. According to this, a film (primary
film) is formed on a surface of the cold-rolled steel sheet.
[0080] An atmosphere gas that is used in the final annealing are
not particularly limited, and a typically used atmosphere gas such
as a gas containing nitrogen and hydrogen may be used. In addition,
as methods or conditions in the annealing separating agent
application and the final annealing, methods or conditions which
are applied to a typical grain-oriented electrical steel sheet may
be employed. For example, as the annealing separating agent, an
annealing separating agent including MgO as a main component may be
used. In this case, a film, which is formed after the final
annealing, contains forsterite (Mg.sub.2SiO.sub.4).
[0081] In the final annealing process, it is preferable that an X
value, which is calculated by the following Expression (2), is set
to 0.0003 Nm.sup.3/(hm.sup.2) or greater. When the X values is to
0.0003 Nm.sup.3/(hm.sup.2) or greater, the film adhesiveness is
further improved.
X=Atmosphere gas flow rate/total steel sheet surface area (2)
Here, the atmosphere gas flow rate represents the amount of the
atmosphere gas that is flowed in when performing box annealing. In
addition, the total steel sheet surface area represents an area of
a steel sheet that is in contact with the atmosphere, and a total
area of a front surface and a rear surface of the steel sheet in a
thin steel sheet.
[0082] The X value, which is calculated by Expression (2), is more
preferably to 0.0005 Nm.sup.3/(hm.sup.2) or greater. On the other
hand, the upper limit of the X value is not particularly limited,
but it is preferable that the X value is set to 0.0030
Nm.sup.3/(hm.sup.2) or less from the viewpoint of the manufacturing
cost.
[0083] <Secondary Film Applying Process>
[0084] An insulating film is applied onto the steel sheet
(cold-rolled steel sheet) on which the primary film is formed.
According to this, a secondary film is formed on the steel sheet.
An application method is not particularly limited, and a method or
conditions which are applied to a typical grain-oriented electrical
steel sheet may be employed.
[0085] <Laser Irradiation Process>
[0086] Laser irradiation may be performed with respect to the steel
sheet, on which the secondary film is formed. When a groove is
formed in the film or a strain is applied to the film through the
laser irradiation, it is possible to further improve magnetic
characteristics of the grain-oriented electrical steel sheet due to
magnetic domain refinement.
[0087] In the grain-oriented electrical steel sheet, which is
manufactured in this manner, a value of a magnetic flux density B8
is 1.92 T or greater. Accordingly, the grain-oriented electrical
steel sheet has excellent magnetic flux density. In addition, film
adhesiveness becomes satisfactory in the steel sheet.
[0088] When the heating conditions, the intermediate annealing
conditions before final cold-rolling, the aging treatment
conditions in the cold-rolling, the heating rate in the
decarburization annealing, and the like are set in appropriate
ranges, the adhesiveness of the film is improved. The reason for
this is not clear, but it is considered that the improvement is
caused by a variation in surface quality of the steel sheet.
[0089] Furthermore, there is no particular limitation to a
measurement method of magnetic characteristics such as the magnetic
flux density and various kinds of iron losses, and the magnetic
characteristics can be measured by a known method such as a method
based on an Epstein test defined in JIS C 2550, and a single sheet
magnetic characteristic test method (single sheet tester: SST)
defined in JIS C 2556.
EXAMPLES
[0090] Hereinafter, a method of manufacturing the grain-oriented
electrical steel sheet according to the present invention will be
described in detail with reference to Examples. The following
Examples are merely examples of the method of manufacturing the
grain-oriented electrical steel sheet according to the present
invention. Accordingly the method of manufacturing the
grain-oriented electrical steel sheet of the present invention is
not limited to the following Examples.
Example 1
[0091] A slab, which contains C: 0.080%, Si: 3.20%, Mn: 0.07%, S:
0.023%, acid-soluble Al: 0.026%, N: 0.0090%, Bi: 0.0015%, and the
remainder including Fe and impurities, was heated to a temperature
T1.degree. C. of 1130.degree. C. to 1280.degree. C. in terms of a
surface temperature, and then retention was performed for 5 hours.
Then, the surface temperature of the slab was lowered to a
temperature T2.degree. C. of 1050.degree. C. to 1220.degree. C.
Then, the surface temperature of the slab was raised to
1350.degree. C., and retention was performed for 20 minutes. Then,
hot-rolling was performed with respect to the slab to obtain a
hot-rolled coil having a thickness of 2.3 mm.
[0092] In addition, intermediate annealing (hot-rolled sheet
annealing), in which retention is performed at a temperature of
1120.degree. C. for 20 seconds, was performed with respect to the
hot-rolled coil and then cold-rolling was performed, and
cold-rolling was performed to obtain a cold-rolled steel sheet
having a thickness of 0.22 mm. Then, decarburization annealing was
performed with respect to the cold-rolled steel sheet under
conditions in which a heating temperature was set to 850.degree. C.
and retention time was set to 120 seconds. A heating rate at this
time was set to 300.degree. C./second.
[0093] Next, an annealing separating agent containing MgO as a main
component was applied onto the cold-rolled steel sheet, and final
annealing was performed in an atmosphere gas containing nitrogen
and hydrogen in a ratio of 3:1 in a state in which a gas flow rate,
that is, atmosphere gas flow rate/total steel sheet surface area
was set to 0.0008 Nm.sup.3/(hm.sup.2). Then, application of a
secondary film (insulating film) was performed.
[0094] With respect to the steel sheet that was obtained, a
magnetic flux density B8 when being magnetized with 800 A/m was
measured by single sheet magnetic measurement (SST) defined in JIS
C 2556, and adhesiveness of the film was evaluated. The film
adhesiveness was evaluated as the following grades A to D. That is,
a case where peeling-off did not occur at a 10.PHI. bending test
was evaluated as A, a case where peeling-off did not occur at a
20.PHI. bending test was evaluated as B, a case where peeling-off
did not occur at a 30.PHI. bending test was evaluated as C, and a
case where peeling-off occurred at a 30.PHI. bending test was
evaluated as D. A and B were determined as passing. In addition,
with regard to the magnetic flux density B8, 1.92 T or greater was
determined as passing.
[0095] Results are illustrated in Table 1. Steel sheet Nos. 3, 5,
and 6 correspond to a manufacturing method that satisfies the
ranges of the present invention, and a magnetic flux density and a
film grade satisfy target values. On the other hand, in steel sheet
No. 1, the slab surface temperature (T1) during heating is lower
than a predetermined temperature, and desired magnetic
characteristics are not obtained. In steel sheet No. 2, the slab
surface temperature (T1) during heating is lower than a
predetermined temperature, and a temperature difference between T1
and T2 is small. Therefore, the desired magnetic characteristics
and film grade are not obtained. In steel sheet No. 4, the
temperature difference between T1 and T2 is smaller than a
predetermined range. Therefore, the desired film grade is not
obtained.
TABLE-US-00001 TABLE 1 SLAB SURFACE STEEL TEMPERATURE SHEET T1 T2
T1 - T2 B8 FILM NO. [.degree. C.] [.degree. C.] [.degree. C.] [T]
GRADE REMARKS 1 1130 1050 80 1.90 B COMPAR- ATIVE EXAMPLE 2 1130
1100 30 1.90 C COMPAR- ATIVE EXAMPLE 3 1200 1140 60 1.92 B PRESENT
EXAMPLE 4 1200 1180 20 1.93 C COMPAR- ATIVE EXAMPLE 5 1280 1180 100
1.93 A PRESENT EXAMPLE 6 1280 1220 60 1.93 B PRESENT EXAMPLE
Example 2
[0096] Slabs, which contain C: 0.080%, Si: 3.20%, Mn: 0.08%, S:
0.025%, acid-soluble Al: 0.024%, N: 0.0080%, Bi: 0.0007% to 0.015%,
and the remainder including Fe and impurities, were heated to a
temperature 1200.degree. C. (T1.degree. C.) in terms of a surface
temperature, and then retention was performed for 5 hours. Then,
the surface temperature of the slab was lowered to a temperature
1100.degree. C. (T2.degree. C.). Then, the surface temperature of
the slab was raised to 1350.degree. C. (T3.degree. C.), and
retention was performed for 30 minutes. Then, the slab was
hot-rolled to obtain a hot-rolled coil having a thickness of 2.3
mm.
[0097] In addition, hot-rolled sheet annealing, in which retention
is performed at a temperature of 1100.degree. C. for 30 seconds,
was performed with respect to the hot-rolled coil and cold-rolling
was performed, and cold-rolling including an aging treatment was
performed to obtain a cold-rolled steel sheet having a thickness of
0.22 mm. At this time, a temperature, time, and the number of times
of the aging treatment were variously changed.
[0098] Then, decarburization annealing was performed with respect
to the cold-rolled steel sheet under conditions in which a heating
temperature was set to 850.degree. C. and retention time was set to
150 seconds. A heating rate in the decarburization annealing was
set to 350.degree. C./second.
[0099] Next, an annealing separating agent containing MgO as a main
component was applied onto the cold-rolled steel sheet, and final
annealing was performed in an atmosphere gas containing nitrogen
and hydrogen in a ratio of 3:1 in a state in which a gas flow rate,
that is, atmosphere gas flow rate/total steel sheet surface area
was set to 0.0006 Nm.sup.3/(hm.sup.2). Then, application of a
secondary film was performed.
[0100] The amount of Bi and aging treatment conditions in the
cold-rolling process are illustrated in Table 2.
[0101] Using the obtained steel sheet, the magnetic flux density B8
when being magnetized with 800 A/m was measured by the single sheet
magnetic measurement (SST), and adhesiveness of the film was
evaluated. An evaluation method and the passing standard were the
same as in Example 1.
[0102] Grades, which represent the magnetic flux density B8 and the
film adhesiveness, are illustrated in Table 2. In addition, a
relationship between the highest temperature in the aging treatment
and the amount of Bi is illustrated in FIG. 1, and a relationship
between the number of times of the aging treatment satisfying
Expression (1), and the number of times of the aging treatment at
130.degree. C. to 300.degree. C. is illustrated in FIG. 2
TABLE-US-00002 TABLE 2 HIGHEST TEMPERATURE IN STEEL SHEET AMOUNT OF
Bi AGING TREATMENT NO. [%] AGING TREATMENT CONDITIONS [.degree. C.]
7 0.0015 100.degree. C. AND 20 MINUTES .times. FIVE TIMES 100 8
0.0015 160.degree. C. AND 20 MINUTES .times. FIVE TIMES 160 9
0.0080 190.degree. C. AND 20 MINUTES .times. FOUR TIMES 190 10
0.0040 250.degree. C. AND 15 MINUTES .times. FIVE TIMES 250 11
0.0150 160.degree. C. AND 30 MINUTES .times. THREE TIMES + 260
260.degree. C. AND 10 MINUTES .times. TWO TIMES 12 0.0015
160.degree. C. AND 5 MINUTES .times. ONE TIME + 200 200.degree. C.
AND 15 MINUTES .times. ONE TIME 13 0.0010 280.degree. C. AND 20
MINUTES .times. TWO TIMES 280 14 0.0007 140.degree. C. AND 15
MINUTES .times. ONE TIME + 230 230.degree. C. AND 45 MINUTES
.times. TWO TIMES 15 0.0080 160.degree. C. AND 60 MINUTES .times.
TWO TIMES + 230 230.degree. C. AND 30 MINUTES .times. TWO TIMES 16
0.0050 160.degree. C. AND 45 MINUTES .times. ONE TIME + 240
240.degree. C. AND 15 MINUTES .times. FOUR TIMES 17 0.0080
160.degree. C. AND 15 MINUTES .times. FOUR TIMES + 290 290.degree.
C. AND 15 MINUTES .times. FOUR TIMES 18 0.0030 160.degree. C. AND
90 MINUTES .times. ONE TIME + 250 250.degree. C. AND 5 MINUTES
.times. THREE TIMES NUMBER OF NUMBER OF TIMES TIMES OF AGING OF
AGING TREATMENTS STEEL SHEET TREATMENTS AT SATISFYING B8 FILM NO.
130.degree. C. TO 300.degree. C. EXPRESSION (1) [T] GRADE REMARKS 7
0 0 1.90 B COMPARATIVE EXAMPLE 8 5 0 1.92 C COMPARATIVE EXAMPLE 9 4
0 1.93 D COMPARATIVE EXAMPLE 10 5 5 1.92 C COMPARATIVE EXAMPLE 11 5
2 1.93 C COMPARATIVE EXAMPLE 12 2 1 1.92 A PRESENT EXAMPLE 13 2 2
1.93 B PRESENT EXAMPLE 14 3 2 1.92 A PRESENT EXAMPLE 15 4 2 1.93 B
PRESENT EXAMPLE 16 5 4 1.93 A PRESENT EXAMPLE 17 5 1 1.92 B PRESENT
EXAMPLE 18 4 4 1.92 A PRESENT EXAMPLE
[0103] As illustrated in steel sheet No. 7, in a case where the
aging treatment was not performed, it was difficult to obtain the
desired magnetic characteristics. As illustrated in steel sheet
Nos. 8 to 10, in a case where the aging treatment at a temperature
satisfying Expression (1) was not performed or the number of times
was great, the film grade became C or D and was poor. In addition,
as illustrated in steel sheet No. 11, in a case where the amount of
Bi was greater than 0.0100%, the film grade became C and was
poor.
[0104] On the other hand, as illustrated in steel sheet Nos. 12 to
18, in a case where the aging treatment conditions were
appropriate, the magnetic characteristics and the film grade were
excellent.
Example 3
[0105] A slab, which contains C: 0.078%, Si: 3.25%, Mn: 0.07%, S:
0.024%, acid-soluble Al: 0.026%, N: 0.0082%, and Bi: 0.0024%, was
heated until the slab surface temperature reached 1180.degree. C.
(T1.degree. C.), and then retention was performed for 1 hour. Then,
the surface temperature of the slab was lowered until reaching
1090.degree. C. (T2.degree. C.). Then, the slab was heated until
the surface temperature of the slab reached 1360.degree. C.
(T3.degree. C.), and retention was performed for 45 minutes. Then,
the slab was hot-rolled to obtain a hot-rolled coil having a
thickness of 2.3 mm.
[0106] In addition, hot-rolled sheet annealing, in which retention
is performed at a temperature of 950.degree. C. to 1150.degree. C.
for 50 seconds, was performed with respect to the hot-rolled coil
and then cold-rolling was performed to obtain a cold-rolled steel
sheet having a sheet thickness of 0.22 mm. Furthermore, in the
cold-rolling, an aging treatment, in which retention is performed
at a temperature of 160.degree. C. for 30 minutes, was performed
two times, and an aging treatment, in which retention is performed
at a temperature of 240.degree. C. for 30 minutes was
performed.
[0107] Then, decarburization annealing was performed with respect
to the cold-rolled steel sheet under conditions in which a heating
temperature was set to 820.degree. C. and retention time was set to
150 seconds. At this time, a heating rate in the decarburization
annealing was set to 20.degree. C./second to 400.degree. C./second.
Next, an annealing separating agent containing MgO as a main
component was applied onto the cold-rolled steel sheet, and final
annealing was performed in an atmosphere gas containing nitrogen
and hydrogen in a ratio of 2:1 in a state in which a gas flow rate,
that is, atmosphere gas flow rate/total steel sheet surface area
was set to 0.0010 Nm.sup.3/(hm.sup.2). Then, application of a
secondary film (insulating film) was performed.
[0108] The intermediate annealing (hot-rolled sheet annealing)
temperature and the heating rate in the decarburization annealing
process are illustrated in Table 3.
[0109] In addition, the magnetic flux density B8 of the obtained
steel sheet and the film grade of the primary film were evaluated
in the same manner as in Example 1 and Example 2. Results are
illustrated in Table 3. FIG. 3 illustrates preferable ranges of the
heating rate in the decarburization annealing and the hot-rolled
sheet annealing temperature.
TABLE-US-00003 TABLE 3 HOT-ROLLED HEATING RATE IN STEEL SHEET
ANNEALING DECARBURIZATION SHEET TEMPERATURE ANNEALING B8 FILM NO.
[.degree. C.] [.degree. C./SECOND] [T] GRADE REMARKS 19 950 100
1.90 C COMPARATIVE EXAMPLE 20 950 350 1.92 C COMPARATIVE EXAMPLE 21
1050 20 1.89 C COMPARATIVE EXAMPLE 22 1050 100 1.92 B PRESENT
EXAMPLE 23 1030 350 1.92 A PRESENT EXAMPLE 24 1150 150 1.92 B
PRESENT EXAMPLE 25 1150 300 1.93 A PRESENT EXAMPLE 26 1100 400 1.93
A PRESENT EXAMPLE
[0110] As illustrated in steel sheet Nos. 19 and 20, when the
hot-rolled sheet annealing temperature was low, the film grade
became C and was poor. In addition, as illustrated in steel sheet
No. 21, when the heating rate in the decarburization annealing was
slow, both of the magnetic characteristics and the film grade were
poor.
[0111] On the other hand, as illustrated in steel sheet Nos. 22 to
26, in a case where the hot-rolled sheet annealing conditions and
the heating rate in the decarburization annealing were in
appropriate ranges, the magnetic characteristics and the film grade
were excellent.
Example 4
[0112] Slabs having a composition (the remainder including Fe and
impurities) illustrated in Table 4 were heated until the surface
temperature reached 1210.degree. C. (T1.degree. C.), and were
retained for two hours. After the surface temperature was lowered
to 1100.degree. C. (T2.degree. C.), the surface temperature was
raised to a temperature (T3.degree. C.) of 1320.degree. C. to
1450.degree. C., and retention was performed for 10 minutes. Then,
hot-rolling was performed to obtain hot-rolled steel sheets having
a sheet thickness of 2.0 mm to 2.4 mm. Intermediate annealing
(hot-rolled sheet annealing), in which retention is performed at a
temperature of 1000.degree. C. to 1150.degree. C. for 10 seconds,
was performed with respect to the hot-rolled steel sheets. A sheet
thickness of some of the annealed steel sheets was set to 0.22 mm
through cold-rolling, and a sheet thickness of the remaining
annealed steel sheets were set to an intermediate sheet thickness
of 1.9 mm to 2.1 mm. Then, intermediate annealing, in which
retention is performed at a temperature of 1080.degree. C. to
1100.degree. C. for 20 seconds, was performed, and cold-rolling was
performed to obtain a sheet thickness of 0.22 ml. In cold-rolling
for obtaining the final sheet thickness, an aging treatment was
performed in which retention is performed at a temperature of
160.degree. C. for 20 minutes, and an aging treatment was performed
in which retention is performed at a temperature of 250.degree. C.
for 5 minutes. The decarburization annealing, in which retention is
performed at a temperature of 800.degree. C. for 180 seconds, was
performed with respect to the cold-rolled steel sheets.
[0113] Next, an annealing separating agent containing MgO as a main
component was applied onto the cold-rolled steel sheets, and final
annealing was performed in an atmosphere gas containing nitrogen
and hydrogen in a ratio of 1:2 in a state in which a gas flow rate,
that is, atmosphere gas flow rate/total steel sheet surface area
was set to 0.0025 Nm.sup.3/(hm.sup.2).
[0114] Then, secondary film application and a magnetic domain
refinement treatment was performed with laser irradiation were
performed.
TABLE-US-00004 TABLE 4 COMPONENTS [mass %] STEEL C Si Mn S Se
sol-Al N Bi Sn Cu Sb Mo A 0.077 3.20 0.07 -- 0.025 0.027 0.0085
0.0075 -- -- 0.03 -- B 0.079 3.15 0.09 0.027 -- 0.027 0.0087 0.0070
0.10 -- -- -- C 0.083 3.29 0.07 0.024 -- 0.024 0.0078 0.0025 0.06
0.10 -- -- D 0.068 3.31 0.09 -- 0.015 0.022 0.0075 0.0085 -- --
0.01 0.02 E 0.072 3.35 0.09 0.010 0.015 0.023 0.0082 0.0050 -- --
-- 0.02 F 0.081 3.30 0.08 0.025 -- 0.022 0.0081 0.0060 -- 0.15 --
--
[0115] Treatment conditions in respective processes are illustrated
in Table 5. In addition, results, which are obtained by evaluating
the magnetic flux density B8 and the film grade in the same manner
as in Examples 1 to 3, are illustrated in Table 5.
TABLE-US-00005 TABLE 5 HOT-ROLLED INTERME- SLAB THICKNESS SHEET
DIATE HEATING OF HOT- ANNEALING INTERME- ANNELAING STEEL TEMPER-
ROLLED TEMPER- DIATE TEMPER- SHEET ATURE SHEET ATURE THICKNESS
ATURE B8 FILM NO. STEEL [.degree. C.] [mm] [.degree. C.] [mm]
[.degree. C.] [T] GRADE REMARKS 27 A 1350 2.5 1050 2.1 1100 1.92 B
PRESENT EXAMPLE 28 A 1450 2.3 1150 -- -- 1.92 B PRESENT EXAMPLE 29
B 1400 2.1 1000 1.9 1080 1.93 B PRESENT EXAMPLE 30 B 1350 2.3 1130
-- -- 1.92 A PRESENT EXAMPLE 31 C 1350 2.0 1090 -- -- 1.92 B
PRESENT EXAMPLE 32 D 1430 2.4 1100 -- -- 1.93 B PRESENT EXAMPLE 33
E 1350 2.4 1100 -- -- 1.92 A PRESENT EXAMPLE 34 F 1320 2.4 1100 --
-- 1.92 B PRESENT EXAMPLE
[0116] As is clear from Table 5, in steel sheet Nos. 27 to 34, the
composition and the conditions of the manufacturing processes were
in predetermined ranges, and desired magnetic characteristics and
film grade were obtained.
[0117] Hereinbefore, a preferred embodiment of the present
invention and examples have been described in detail with reference
to the accompanying drawings, but the present invention is not
limited to the examples. It should be understood by those skilled
in the art that various modification examples and variation
examples can be made without departing from the range of the
technical sprit described in the appended claims, and pertain to
the technical scope of the present invention.
INDUSTRIAL APPLICABILITY
[0118] According to the present invention, it is possible to obtain
a grain-oriented electrical steel sheet having excellent magnetic
characteristics while improving adhesiveness of a primary film at a
low cost.
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